Infrared-enhanced selective catalytic reduction of NOx

ABSTRACT

This invention relates to a device and method using infrared to enhance selective catalytic reduction (SCR) of NOx, consisting of at least an infrared-emitting body, said infrared-emitting body being engineered to have specific spectral luminance covering a part or the whole of 3-14 μm wavelength range, that provides an effective means for improving NOx conversion in the SCR aftertreatment system of diesel engines.

BACKGROUND

1. Field of the Invention

This invention relates to a device and method using infrared to enhanceselective catalytic reduction (SCR) of NOx, consisting of at least aninfrared-emitting body, said infrared-emitting body being engineered tohave specific spectral luminance covering a part or the whole of 3-14 μmwavelength range, that provides an effective means for improving NOxconversion in the SCR aftertreatment system of diesel engines.

2. Description of Prior Art

The combustion of fossil fuel always leads to the formation of nitrogenoxides (NOx). NOx formation mechanisms in internal combustion enginesare well known and details published in textbooks. The term “NOx” isused primarily to describe two species: nitric oxide (NO) and nitrogenoxide (NO₂). Sometimes the term is extended to include other oxides suchas a nitrous oxide (NO₂), which is insignificant and often ignored.

The most desirable removal mechanism would be direct decomposition ofNOx. The selective catalytic reduction (SCR) is a validated technologyfor the removal of NOx in diesel exhaust. There are commercial exhaustaftertreatment systems that employ intentional injection of somereducing agent into the exhaust gas. This is called “active deNOx”. Thereducing agent is usually ammonia or urea, while some researchers arepursuing methods using hydrocarbons as reducing agent.

The strategy of urea-SCR is to set free NH₃ from urea, CO(NH₂)₂, bythermolysis and hydrolysis as given in the chemical equation (1):

CO(NH₂)₂→HNCO+NH₃. . . (by thermolysis)

HNCO→NH₃+CO₂. . . (by hydrolysis)   (1)

The NH₃ radical then reacts with NO and NO₂ as depicted in chemicalequations (2) and (3):

6NO+4NH₃→5N₂+6H₂O   (2)

6NO₂+8NH₃→7N₂+12H₂O   (3)

An undesired byproduct, such as biuret (NH₂CONHCONH₂), can be producedif urea solution is not properly thermolyzed or hydrolyzed.

An alternative method is the use of a light hydrocarbon, such aspropylene, propane, or methane as a reluctant during the selectivecatalytic reduction of NOx (HC—SCR). As such, hydrocarbons can beprovided from the fuel source, thus adding no new storage,transportation or corrosion concerns. For example, the propylene C₃H₆reacts with NO in the way as described in chemical equation (4)

2C₃H₆+18NO→9N₂+6H₂O+6CO₂   (4)

The present inventor had realized the scientific fact that hydrocarbonsare “infrared-active” and absorb infrared photons shorter than 20 μm inwavelengths causing vibrations, which resulted in the inventions of fuelcombustion enhancement devices as described in U.S. Pat. Nos. 6,026,788and 6,082,339 (by the present inventor). Quantum Mechanically speaking,infrared-excited hydrocarbon molecules have lower activation barriersand thus get higher chemical reaction rates. The present inventor haddeveloped several infrared-emitting bodies in 3-14 μm wavelengths, whichare categorized as “mid-infrared” in NASA definition but “far-infrared”in Japanese convention. The present inventor was able to use theIR-emitters to validate underlying science of infrared-excitation inMethane-Air Counterflow Flame experiments. Infrared was found helpingimprove 6 % combustion efficiency in combustion of methane-air mixtureas described in reaction (5).

CH₄+O₂→CO+H₂+H₂O

furthermore H₂+½O₂→H₂O

CO+½O₂→CO₂   (5)

In real diesel engine applications, the present inventor discoveredexperimentally that such IR-emitters could also enhance the reductionreaction described in equation (4) for removal of NOx. Throughliterature search, the present inventor further realized that the bondsin urea and ammonia molecules, including N—H, —NH₂, —CONH—, and —CONH₂,also absorb infrared in 3-14 μm wavelengths to cause molecularexcitations. In other words, urea and ammonia are so-called“infrared-active”.

For example, —HNCO—bond vibrates at 3.23-3.26 and 6.45-6.62 μm bands,while the —NH₂ bonds absorb photons at 3.029 μm, 3.106 μm, and 6.680 μmwavelengths to respectively cause symmetric, asymmetric, and bendingvibrations. The vibrational modes also include overtones at bands4.52-4.72, 6.58-6.76, 9.57-9.85, 11.90-12.50, and 12.20-12.99 μm, whichall fall in said 3-14 μm wavelength range. It became evident thatinfrared can help enhancing urea-SCR reaction in equations (1), (2), and(3), and HC—SCR in equation (4), because all reactants in the equationare all infrared-active. Besides, the bonds of biuret (NH₂CONHCONH₂) arefound to vibrate at 4.72-4.93 and 6.80-6.92 μm bands so that infraredexcitation may raise reduction of biuret and limit its production in theprocesses.

As previously mentioned, the present inventor had discovered the use ofinfrared in 3-14 μm wavelengths for improving combustion efficiency ofhydrocarbon fuel in internal combustion engines as disclosed in U.S.Pat. Nos. 6,026,788 and 6,082,339 by the present inventor. Since then, anumber of similar inventions had followed, for examples U.S. Pat. Nos.7,021,297, 7,036,492, and 7,281,526, just to name a few. Even so, theprior arts only described the use of infrareds in oxidation ofhydrocarbons and failed to teach the use of infrareds for aidingselective catalytic reduction (SCR) of NOx using urea, ammonia, andhydrocarbons as reducing agents in diesel applications.

Objects and Advantages

Accordingly, one object of this invention is to provide a device andmethod that can increase the efficiency of a selective catalyticreduction (SCR) of NOx aftertreatment using urea, ammonia, hydrocarbons,or other infrared-active substances as reducing agent(s).

Another object of the present invention is to provide a simple,easy-to-implement, and maintenance-free infrared-enhanced SCR of NOxdevice.

These objectives are achieved by an infrared-enhanced SCR devicecomprising essentially at least one infrared emitting body havingspecific spectral luminance covering a part or whole of 3-14 μmwavelength range. The device can be disposed in the delivery system ofreducing agent for said SCR system to excite the reluctant before itmixes with exhausts gas for reduction of NOx.

Other objects, features and advantages of the present invention willhereinafter become apparent to those skilled in the art from thefollowing description.

DRAWINGS FIGURES

FIG. 1 shows a cross-sectional view of one embodiment of the presentinvention with a tubular infrared-emitting body implemented as a part ofnozzle assembly.

FIG. 2 shows a cross-sectional view of another embodiment of the presentinvention with an infrared emitting body in partial-tubular form andbeing mounted on a supply hose.

REFERENCE NUMERALS IN THE DRAWINGS

-   11 Infrared emitting body-   21 Nozzle assembly-   22 Supply hose

SUMMARY

In accordance with the present invention an infrared-enhanced selectivecatalytic reduction (SCR) of NOx aftertreatment device and methodconsists of at least an infrared emitting body having specific spectralluminance covering a part or the whole of 3-14 μm wavelength range. Itcan enhance NOx conversion efficiency of said SCR system, resulting inreduced NOx in exhaust. The infrared emitting body can be disposed inthe passageway of reducing agent for said SCR aftertreatment to energizethe reluctant before it mixes with exhaust gas for NOx reduction.

DETAILED DESCRIPTION OF THE INVENTION

It is well known that absorption of an infrared photon at a wavelengthshorter than 20 μm (micrometer) gives rise to bond stretching or bendingvibration in molecules that are “infrared-active”. In fact, OrganicChemists have been using IR absorption spectral analysis (so-called“Infrared Correlation Charts”) to identify unknown specimens fordecades. Based on spectral absorption profiles in 3-7 μm (so-called“Functional Group” zone) and 7-20 μm (“Signature” zone) the testspecimen can be precisely identified. However, what people had longignored was absorbing IR photons can increase kinetic energy of covalentbonds and thus cause molecule to vibrate. It not only changes dipolemoment of the molecule, but also decreases activation barrier of thebond and thus increases reaction chemical rate, which is described inequation (6) by Quantum Mechanics:

Reaction Rate: W=Ke^(−E/RT)   (6)

where K is a constant, E activation energy, and T temperature (inKelvin). Equation (6) predicts an increased reaction rate W with areduced activation energy E.

The present inventor had reported favorable results on using the devicesas described in U.S. Pat. No. 6,026,788 to excite fuels for enhancedengine performance. The net results were improved fuel combustionefficiency with increased torque/power, reduced fuel consumption, andlowered emissions. In real diesel engine applications the presentinventor recognized that the reducing agents such as urea, ammonia, orhydrocarbons used in commercial urea-SCR or HC—SCR aftertreatmentsystems for removal of NOx are all “infrared-active”. In urea andammonia, bonds such as N—H, —NH₂, and primary and secondary amide —CONH₂show strong absorption for combination and overtone modes in 3-7 μmwavelengths (i.e. Zone I). There are other overtone bands in longwavelengths, but often too weak to be noticed.

The present inventor learned from Japanese published results andexperimentally confirmed that adding cobalt oxide and/or nickel oxidesto the oxide mixture as disclosed in U.S. Pat. No. 6,026,788 can boostthe radiation strength at short wavelengths. Meanwhile, increasingceramic processing temperature from a conventional 1200° C. to above1350° C. can further strengthen spectral luminance of the resultantIR-emitter at short wavelengths. Accordingly, several examples of thepresent invention were prepared for demonstration.

FIG. 1 shows a cross-sectional view of one embodiment of the presentinvention, in which an infrared-emitting body 11 takes a tubular formand is disposed as a part of the nozzle assembly 21 that is connected toa supply line 22 for injecting reducing agent into the SCR system. Inthis implementation the infrared-emitting body is in direct contact withreducing agent. By the same token, the infrared-emitting body can beimmerged in the storage tank of the reducing agent as an alternative toprovide infrared excitation.

FIG. 2 shows a cross-sectional view of another embodiment of the presentinvention, in which a partial-tubular infrared-emitting body 11 ismounted on a supply line 22 connecting to the nozzle assembly 21. Inthis arrangement, the infrared-emitting body can be mounted on theexterior of a nonmetal section of the supply line for ease ofimplementation. Infrared photons can penetrate nonmetal hose and excitethe substance flowing through the line. Such implementation does notrequire infrared-emitting body to directly contact reducing agent.

In other embodiments the infrared emitting bodies can be disposed in theinterior of a supply line or nozzle assembly by embedding or coating onthe inner wall, or being a part of the reducing agent delivery system.

EXAMPLES

Several demonstration samples were made with 40 (weight) % silicate, 25%alumina, 17% zirconia, 7% magnesium oxide, 5% cobalt oxide, and otherminor elements and processed at a temperature above 1350° C. An SEM/EDS(scanning electron microscope with energy dispersive spectrometry) plotwas run with the samples to obtain a quantitative analysis on theelemental composition of the oxide compounds. In lab, an infraredimaging camera with variable wavelength band filters was used todetermine the spectral luminance for these IR-emitters. The IR-emitterwas tested by mounting it on a Teflon fuel hose to an HC—SCR system witha zeolites catalyst. The preliminary test result seemed veryencouraging, while further scientific investigation remained to be done.

Conclusion, Ramifications, and Scope

According to the present invention, an infrared-enhanced selectivecatalytic reduction (SCR) device comprises at least an infrared emittingbody having specific spectral luminance covering a part or the whole of3-14 μm wavelength range, which can be disposed in the passageway of thereducing-agent to said SCR system for better NOx conversion.

The invention has been described above. Obviously, numerousmodifications and variations of the present invention are possible inlight of the above teachings. Such variations are not to be regarded asa departure from the spirit and scope of the invention and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. An infrared-enhanced selective catalytic reduction (SCR) device forexciting the reducing agent and for thereby achieving efficient NOxreduction, said device consisting essentially an SCR mechanism and atleast one infrared emitting body, said infrared emitting body havingspecific spectral luminance covering a part or the whole of 3-14 μmwavelength range.
 2. A device according to claim 1 wherein the infraredemitting body is made of oxides selected from the oxides of Groups I,II, III, IV, or Transition elements in Periodic Table, or a mixture ofsaid oxides.
 3. A device according to claim 1 wherein one reducing agentfor said SCR mechanism is ammonia or urea.
 4. A device according toclaim 1 wherein one reducing agent for said SCR mechanism is hydrocarbonor other infrared-active substance.
 5. A device according to claim 1wherein the infrared emitting body is disposed adjacent to or in contactwith said reducing agent.
 6. A device according to claim 1 wherein theinfrared emitting bodies is disposed at exterior of a delivery hose ofreducing agent.
 7. An infrared-enhanced selective catalytic reduction(SCR) method for exciting reducing agent and for thereby achievingefficient NOx reduction comprising: providing an SCR mechanism withinfrared-active reducing agent and at least an infrared-emitting bodyhaving specific spectral luminance covering a part or the whole of 3-14μm wavelength range, and disposing said infrared-emitting body adjacentto or in contact with said reducing agent.